The present invention relates to an apparatus for freeing a one-way switch of high power dissipation stresses during turn-on and turn-off, the electronic one-way switch being connected between a voltage source and a load, and wherein an inductive storage element and a capacitive storage element are disposed in a shunt circuit of the electronic one-way switch and a free wheeling diode is provided in the load-side circuit for taking over the load current when the one-way switch is turned off. Such an apparatus is known from German Pat. No. 2,905,782.C2.
Electronic one-way switches must be protected against excessive power dissipation stresses during turn-off, particularly if the switching frequencies are high. For this purpose, it is customary to provide a limiting network in a shunt circuit of the one-way switch. In a no-loss design, this limiting network is composed of inductive and capacitive elements and of diodes; see, for example, "Protection of Power Transistors in Electric Vehicle Drives" by Thomas A. Radomski, 1982, IEEE Conf. Rec., pages 455-465; and German Patent Application No. 2,644, 715.A1. When the one-way switch is turned off, these limiting networks take over the dissipated power in storage elements and thus protect the one-way switch. When the electronic switch is turned on again, these storage elements are recharged and are available to take up energy when the one-way switch is turned off again.